Actions, combat, for beginners

The advantage of handling it this way, in my view, is that decisions about cancellation etc. are only about what cards you have in hand. In particular, since Wakes are specifically playable in the cancellation window(*), if they were replaceable, life could get awkward in terms of players trying to calculate whether they might draw into that cancellation minion card. As it is, everyone just looks at their hand and decides whether or not they can cancel the card, simplifying things.

It can get a little messy if you're in the habit of replacing cards quickly and/or other players on the table are less quick to say "Hang on a sec... Yeah, I'm going to cancel that", and so you may have to rewind things occasionally. But on balance, I think that's the better trade-off. If playing something obviously controversial, or where you really want to avoid rewinding, you can of course pause and ask the table for cancellations explicitly rather than implicitly.

(*) See the rulebook, in the bit between 1.6.1.1 and 1.6.1.2: "Some effects can cancel a card "as it is played." These effects as well as wake effects (see Special Terms, sec. 11) are the only effects allowed during the "as played" time period of another card. Even drawing to replace cards comes after this time period."

Got?
It has been like that for quite a long time/always, people just tend to play bit more streamlined.

If you want to be super certain you'd need to ask after every card you play if someone wants to cancel them lest they start complaining that they didn't get a chance to do so. Probably happens once in 20-30 games so it just ain't worth it.

Long time ago in the EC at Heidelberg I remember playing against Kamel the first time and he did play a cancel deck magnificently, always observing what was happening on the table and then quickly, clearly and audibly saying "stop" before the player who had played a card had a chance to redraw. Then we discussed if he should use the "DI or Sudden he had in his hand". Certainly the clearest and best play I've ever seen.

(Well, effectively he was also playing time as to get his Week of Nightmares hit in the late game without the game actually having progressed hat far. But perfectly within the rules.)

In magic tournaments I've noticed a pretty good mannerism to go with such cards.

You say "stop!" or "wait" immediately when you have the opportunity to cancel/counter, and only THEN ponder whether you actually want to commit to countering/canceling. If not, you just say "ok, continue", otherwise "I counter/cancel that". This ensures that no backtracking is needed, and as long as this is done in moderation (not to just mess with people, in which case you would get warning for delaying the game) it keeps things both in control, within the rules, and moving along smoothly. Of course you shouldn't do this with every single card opponents play, but only when it would be meaningful for you to cancel their card.

Of course, since you don't need an actual card to say "Wait. Ok, continue", this can be done to bluff people as well, and they can't be sure whether you actually HAVE a cancel card, unless you are super obvious about it.

"Do you believe in the power of the night?
If you want to go with me, refuse the light"
- Blutengel, Soultaker